Regulation of the air and fuel mixture supplied to an internal combustion engine, particularly an engine of the compression ignition type, has received widespread attention. Unless a satisfactory air/fuel ratio is achieved in the engine cylinders, engine operation will be adversely affected and fuel economy will be reduced. Proper regulation of the air/fuel mixture, moreover, can eliminate or reduce substantially undesirable emission components from the engine exhaust. If air and fuel are supplied to the cylinders in a carefully controlled ratio which will allow complete combustion to occur under all operating conditions, apparatus for removing exhaust emissions to achieve acceptable vehicle emission control can be entirely eliminated. In addition, efficient and economic engine operation will be realized as well.
Fuel systems for internal combustion engines wherein the fuel supplied to the engine is controlled in response to intake manifold pressure are well known. Many such systems include a source of fuel under pressure, e.g., a fuel pump, and a mechanism for regulating the pressure of the fuel supplied to an injector located at each cylinder. To achieve optimum fuel/air ratios under all operating conditions, highly sophisticated refinements have been made in these basic components to permit a carefully scheduled pressure output as a function of operator demand and engine speed. U.S. Pat. Nos. 4,187,817 to Wilson et al. and 4,248,188 to Wilson et al. are illustrative of such systems. The air/fuel control systems described in these patents mechanically modulate the flow of fuel into the engine in response to the pressure of the air in the intake manifold, which varies from a "no-air" condition below the rated pressure level to the full rated pressure. Both systems employ a diaphragm or flexible bellows operator for a fuel flow modulating valve responsive to engine intake manifold air pressure as sensed through an air line connecting the diaphragm operator with the intake manifold. The diaphragm is biased by a single spring selected and calibrated to provide modulation of the valve restriction to vary the fuel pressure in response to intake manifold pressure whereby the optimum air/fuel ratio can be maintained over a broad range of operating conditions. A drain line is additionally included in these systems to provide a fluid connection between the air fuel control mechanism and the engine fuel tank.
The air fuel control system disclosed in U.S. Pat. No. 4,187,817 further includes a flow restrictor in the air line to prevent engine fuel tank pressurization and reverse fuel flow into the engine's intake manifold in the event of a rupture of the diaphragm operator. The air fuel control system of U.S. Pat. No. 4,248,188 includes, in addition, an attenuator assembly which attenuates the transient response of the diaphragm operator by causing fuel to be supplied to a control chamber at a rate which is greater than that at which fuel is discharged from the chamber. While these air fuel control systems generally achieve an adequate air/fuel ratio, very precisely controlled metering of fuel is difficult to achieve and, hence, an optimum air/fuel ratio is not always realized for all engine operating conditions. Moreover, the variations in back pressure which have been characteristic of these prior art air fuel controls have caused air fuel control delay variations and, consequently, response problems. Further, engines intended for marine applications have not been able to em ploy the kind of drain line disclosed by the prior art air fuel controls. In the event of a diaphragm failure in a prior art air fuel control of the kind described in the aforementioned patents in a marine engine, fuel would tend to collect in the bilge.
Other air fuel control systems which employ diaphragm operators are also known in the prior art. For example, U.S. Pat. No. 3,795,233 to Crews et al. discloses a control device for a super-charged engine having a governor means connected to a fuel-adjusting member and a supercharger which supplies air to the engine through an intake manifold. Three spring members are employed in this system to balance forces on the diaphragm when there is no pressure in the control system chamber on the intake manifold side of the diaphragm. This system is responsive to both intake air pressure and engine oil pressure to override the governor means. However, the system described in this patent does not include a fuel flow modulating valve, but employs a mechanical linkage to vary the fuel supplied to the engine upstream of the throttle.
None of the air fuel control devices disclosed by the prior art, moreover, is completely tamper-resistant. Improper tampering with an internal combustion engine fuel supply adversely affects both fuel economy and long term engine durability. Fuel systems of the type described in the aforementioned patents generally include a drain line to the fuel tank for returning fuel which is not injected into the engine cylinders or which is bled from the gear pump section of the fuel pump and an adjustable air screw in the fuel pump. It is widely known that the short terms power output of engines equipped with such fuel system can be increased by clamping off this drain line and opening the air screw. However, the effects of such unauthorized modification can be extremely adverse, including loss of fuel economy and shortened engine life. In addition, such unauthorized adjustments will cause engine emissions to vary from those achieved by the air fuel control settings set by the engine manufacturer so that the engine does not comply with governmentally established emissions standards.
The prior art, therefore, fails to disclose an air fuel control for an internal combustion engine which responds quickly to meter a controlled, optimum amount of fuel in response to intake manifold air pressure and which cannot be adjusted or otherwise modified while the air fuel control remains mounted on the engine.